1. Field of the Invention
This invention relates to an adapter for use with clamping devices for clamping workpieces on perforated screen plates of machine tools.
2. Description of Prior Art
Machine tools, such as milling machines or drills, are often equipped with a clamping table for clamping workpieces. Previously, these tables mostly had T-grooves or dovetailed grooves, into which clamping screws or threaded bolts were inserted. The workpiece was fastened either by these threaded bolts or with other clamping elements, such as clamping straps and threaded clamps. This type of clamping table is increasingly being replaced by machine tables having a screen plate or a screen block. Both variants have threaded bores at defined distances in the perforated screen. Typical distances between holes of the perforated screen are 50 mm with an accuracy of a few micrometers. The workpiece can be fastened as before with the aid of clamping elements, which are mounted in the holes of the perforated screen with screws.
Situations occur where the position of the holes provided in the screen is unsatisfactory.
This is the case, for example, if it is necessary to clamp a workpiece in such a way that poor force transfer conditions are created. In such situations the lever arm between the clamping screw of the clamping element and the workpiece is larger than the lever arm of the clamping element on the opposite side of the clamping screw. Thus, the clamping force is transferred in an unfavorable manner to the workpiece. The workpiece is not securely clamped, and accuracy and the clamping force are reduced.
The locations of the screen holes provided often cause the clamping element to cover a portion of the workpiece surface to be treated. Thus, in these situations it is necessary to clamp the workpiece twice for treatment. This increases the amount of labor and therefore production costs and, in addition, greater production tolerances in the workpiece must be expected.
In both of the situation mentioned a threaded hole is needed exactly in a place where there is none, namely between two adjoining holes of the perforated screen plate.